NONLINEAR-ANALYSIS OF THE HIPPOCAMPAL SUBFIELDS OF CA1 AND THE DENTATE GYRUS

The paper discusses the use of nonlinear bispectral analysis in examin ing the hippocampal EEG collected at subfields of CA1 and the dentate gyrus during the vigilance state of REM sleep. The cross-bispectrum an d its unique capabilities of detecting and quantifying quadratic nonli near interactions occurring between these two hippocampal subfields ar e explained and demonstrated with simulation examples and EEG data. It was found in this study that quadratic nonlinear interactions exist b etween CA1 and the dentate gyrus in the 6-8 frequency band which domin ates the theta (theta) rhythm observed in the hippocampal EEG during R EM sleep. As a result, energy components around the frequency band of the second-order harmonics of theta rhythm are not totally spontaneous , but generated largely due to quadratic nonlinear interactions.